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USGS2020

Calibration of carbonate-water triple oxygen isotope fractionation: Seeing through diagenesis in ancient carbonates

High precision triple oxygen isotope measurements of carbonates can better constrain temperatures and oxygen isotope compositions of seawater through geologic time than 18 O/ 16 O measurements alone, but lack of a definitive calibration has hindered progress. In this study, we fluorinated both carbonate and water samples to measure quantitatively the triple oxygen isotope composition of each phase. We compared the oxygen isotope fractionation between carbonate and water for different carbonate materials: calcite synthesized with and without carbonic anhydrase, abiogenic calcite from Devils Hole, and extant biogenic calcite and aragonite of marine origin. We found similar 1000 lnα 18 O cc-wt values for all materials and combined the results with the high temperature experimental data of O'Neil et al. (1969) , resulting in the following fractionation equation ( T in Kelvins) 1000 ln α 18 O cc - w t = 2.84 ( ± 0.02 ) × 10 6 T 2 - 2.96 ( ± 0.19 ) "> 1000lnα18Occ-wt=2.84(±0.02)×106T2-2.96(±0.19) . The calcite triple oxygen isotope values yielded a θ - T relationship of θ cc-wt = –1.39(±0.01)/ T + 0.5305 whereas the aragonite triple oxygen isotope values yielded a θ - T relationship of θ ara-wt = –1.53(±0.02)/ T + 0.5305. The calcite-water triple oxygen isotope equilibrium fractionation equation for natural samples is Δ 17 ′ O cc - Δ 17 ′ O wt = 2.84 ( ± 0.02 ) × 10 6 T 2 - 2.96 ( ± 0.19 ) - 1.39 ( ± 0.01 ) T + 0.5305 - λ "> Δ17′Occ-Δ17′Owt=2.84(±0.02)×106T2-2.96(±0.19)-1.39(±0.01)T+0.5305-λ . The combined 1000 lnα 18 O and 1000 lnα 17 O relationships can be used to assess equilibrium in ancient samples and to evaluate potential secular changes in the δ 18 O value of seawater. Most of the Phanerozoic samples analyzed in this study, which were determined to be pristine in previous studies, have undergone some level of diagenesis. Two samples appear to preserve their original oxygen isotope compositions and suggest a cool ocean with a δ 18 O value similar to the modern ocean. Using a fluid-rock interaction model, we can “see through” the diagenetic process and estimate the triple oxygen isotope composition of the carbonate prior to alteration. In doing so, we show that for the time intervals and sample locations measured in this study, Phanerozoic oceans had a comparable range of oxygen isotope compositions and temperatures as modern seawater.

Geochemica et Cosmochimica Acta↗

USGS1980

Declination and inclination errors in experimentally deposited specularite-bearing sand

Naturally disaggregated specularite-bearing sandstone from the Triassic Moenkopi Formation, artificially deposited in controlled magnetic fields of ∼5 × 10 −2 mT, acquires a stable remanent magnetization that has systematic errors in inclination and declination. Inclinations about 12° shallower than the applied fields are produced by deposition on a horizontal surface in still water. Deposition from flowing water on a surface inclined 6–10° results in inclination errors of as much as 20°. Water flowing obliquely to the applied field results in declination errors of about 10°, with declinations systematically rotated toward the upstream direction of current flow. These experimental results indicate that specularite-bearing sediment responds to the earth's field in a manner similar to magnetite-bearing sediment, and support observational evidence for a primary magnetization of depositional origin in specularite in red beds of the Moenkopi Formation.

Earth and Planetary Science Letters↗

USGS2015

Surprise and opportunity for learning in Grand Canyon: the Glen Canyon Dam Adaptive Management Program

With a focus on resources of the Colorado River ecosystem below Glen Canyon Dam, the Glen Canyon Dam Adaptive Management Program has included a variety of experimental policy tests, ranging from manipulation of water releases from the dam to removal of non-native fish within Grand Canyon National Park. None of these field-scale experiments has yet produced unambiguous results in terms of management prescriptions. But there has been adaptive learning, mostly from unanticipated or surprising resource responses relative to predictions from ecosystem modeling. Surprise learning opportunities may often be viewed with dismay by some stakeholders who might not be clear about the purpose of science and modeling in adaptive management. However, the experimental results from the Glen Canyon Dam program actually represent scientific successes in terms of revealing new opportunities for developing better river management policies. A new long-term experimental management planning process for Glen Canyon Dam operations, started in 2011 by the U.S. Department of the Interior, provides an opportunity to refocus management objectives, identify and evaluate key uncertainties about the influence of dam releases, and refine monitoring for learning over the next several decades. Adaptive learning since 1995 is critical input to this long-term planning effort. Embracing uncertainty and surprise outcomes revealed by monitoring and ecosystem modeling will likely continue the advancement of resource objectives below the dam, and may also promote efficient learning in other complex programs.

Arizona, Nevada, Utah↗

USGS2006

Flume experiments on the alignment of transverse, oblique, and longitudinal dunes in directionally varying flows

For more than a century geologists have wondered why some bedforms are orientated roughly transverse to flow, whereas others are parallel or oblique to flow. This problem of bedform alignment was studied experimentally using subaqueous dunes on a 3–6-m-diameter sand-covered turntable on the floor of a 4-m-wide flume. In each experiment, two flow directions (relative to the bed) were produced by alternating the turntable between two orientations. The turntable was held in each orientation for a short time relative to the reconstitution time of the bedforms; the resulting bedforms were in equilibrium with the time-averaged conditions of the bimodal flows. Dune alignment was studied for five divergence angles (the angle between the two flow directions): 45°, 67–5°, 90°, 112–5° and 135°. The flow depth during all experiments was approximately 30 cm; mean velocity was approximately 50 cm s -1 and mean grain diameter was 0–6 mm. Each experiment continued for 30–75 min, during which time the flume flow was steady and the turntable position changed every 2 min. At the end of each experiment, water was slowly drained from the flume and dune alignment was measured. Transverse dunes (defined relative to the resultant transport direction) were created when the divergence angle was 45° and 67–5°, and longitudinal dunes were created when the divergence angle was 135°. At intermediate divergence angles, dunes with both orientations were produced, but transverse dunes were dominant at 90°, and longitudinal dunes were dominant at 112–5°. One experiment was conducted with a divergence angle of 135° and with unequal amounts of transport in the two flow directions. This was achieved by changing the orientation of the turntable at unequal time intervals, thereby causing the amount of transport to be unequal in the two directions. The dunes formed during this experiment were oblique to the resultant transport direction. These experimental dunes follow the same rule of alignment as wind ripples studied in previous turntable experiments. In both sets of experiments, the bedforms developed with the orientation having the maximum gross bedform-normal transport (the orientation at which the sum of the bedform-normal components of the two transport vectors reaches its maximum value). In other words, the bedforms develop with an orientation that is as transverse as possible to the two flows. In those cases where the two flows diverge by more than 90° and transport equal amounts of sand, bedforms that are as transverse as possible to the two separate flows will be parallel to the resultant of the two flow vectors. Although such bedforms have been defined by previous work as longitudinal bedforms, they are intrinsically the same kind of bedform as transverse bedforms.

Sedimentology↗

USGS2026

Effects of a low-lipid diet on the gut microbiome and head kidney transcriptome of juvenile Chinook Salmon

Objective Pacific salmon Oncorhynchus spp. reared in production hatcheries are typically fed high-lipid, energy-dense diets to achieve large size and high body condition prior to release. In contrast, juveniles in natural environments tend to consume low-lipid, high-protein diets, and fish reared for research or conservation purposes are sometimes fed diets that are formulated to mimic natural diets and promote wild-like phenotypes. Understanding how these alternative diets affect fish health beyond growth and body condition could ultimately contribute to improving hatchery fish fitness. Methods In this work, we evaluated changes in the fecal microbiome and gene expression of juvenile Chinook Salmon O. tshawytscha on a standard high-lipid hatchery diet versus a low-lipid diet formulated to mimic the nutrition profile of natural-origin fish. To evaluate the time scale at which diet alters the fecal microbiome, we collected longitudinal samples over a 12-week period and switched the diets of a subset of fish twice during the experiment. We used 16S ribosomal RNA gene amplicon sequencing to characterize fecal microbiome differences between fish on the two diets as well as hatchery-reared fish at a production hatchery, hatchery fish that had been captured after release into a stream, and natural-origin, stream-reared fish of similar ages. Additionally, we conducted RNA sequencing on head kidney samples from laboratory-reared fish to evaluate changes in gene expression in this important immune organ. Results We found that the low-lipid diet and the hatchery diet resulted in microbiomes that differed from the microbiome of natural-origin fish and from each other and that diet-driven changes to the microbiome could occur in under 14 d. The low-lipid diet did not result in a microbiome that resembled the microbiome of naturally produced fish. Instead, the low-lipid diet resulted in a microbiome community that was distinct from those of fish reared on the hatchery diet and fish sampled from the wild. The RNA sequencing results indicated differential enrichment of pathways related to immunity, metabolism, and hormone synthesis between fish that were fed the two experimental diets. Conclusions The results suggest that additional environmental factors influence the microbiome more strongly than diet formulation or that the low-lipid diet has a smaller effect on the microbiome than a natural, invertebrate-based diet. Given that the gut microbiome and systemic immune function contribute significantly to disease resistance, our findings highlight the importance of understanding how diets fed to fish in captivity may affect fish health beyond growth and body condition metrics.

Journal of Aquatic Animal Health↗

USGS2009

Net Loss of CaCO3 from a subtropical calcifying community due to seawater acidification: Mesocosm-scale experimental evidence

Acidification of seawater owing to oceanic uptake of atmospheric CO 2 originating from human activities such as burning of fossil fuels and land-use changes has raised serious concerns regarding its adverse effects on corals and calcifying communities. Here we demonstrate a net loss of calcium carbonate (CaCO 3 ) material as a result of decreased calcification and increased carbonate dissolution from replicated subtropical coral reef communities (N=3) incubated in continuous-flow mesocosms subject to future seawater conditions. The calcifying community was dominated by the coral Montipora capitata. Daily average community calcification or Net Ecosystem Calcification (NECC=CaCO 3 production - dissolution) was positive at 3.3 mmol CaCO 3 m -2 h -1 under ambient seawater pCO 2 conditions as opposed to negative at -0.04 mmol CaCO 3 m -2 h -1 under seawater conditions of double the ambient pCO 2 . These experimental results provide support for the conclusion that some net calcifying communities could become subject to net dissolution in response to anthropogenic ocean acidification within this century. Nevertheless, individual corals remained healthy, actively calcified (albeit slower than at present rates), and deposited significant amounts of CaCO 3 under the prevailing experimental seawater conditions of elevated pCO 2 .

Biogeosciences↗

USGS2011

40Ar∗ loss in experimentally deformed muscovite and biotite with implications for 40Ar/39Ar geochronology of naturally deformed rocks

The effects of deformation on radiogenic argon ( 40 Ar ∗ ) retentivity in mica are described from high pressure experiments performed on rock samples of peraluminous granite containing euhedral muscovite and biotite. Cylindrical cores, ∼15 mm in length and 6.25 mm in diameter, were drilled from granite collected from the South Armorican Massif in northwestern France, loaded into gold capsules, and weld-sealed in the presence of excess water. The samples were deformed at a pressure of 10 kb and a temperature of 600 °C over a period 29 of hours within a solid medium assembly in a Griggs-type triaxial hydraulic deformation apparatus. Overall shortening in the experiments was approximately 10%. Transmitted light and secondary and backscattered electron imaging of the deformed granite samples reveals evidence of induced defects and for significant physical grain size reduction by kinking, cracking, and grain segmentation of the micas. Infrared (IR) laser (CO 2 ) heating of individual 1.5–2.5 mm diameter grains of muscovite and biotite separated from the undeformed granite yield well-defined 40 Ar/ 39 Ar plateau ages of 311 ± 2 Ma (2σ). Identical experiments on single grains separated from the experimentally deformed granite yield results indicating 40 Ar ∗ loss of 0–35% in muscovite and 2–3% 40 Ar ∗ loss in biotite. Intragrain in situ ultraviolet (UV) laser ablation 40 Ar/ 39 Ar ages (±4–10%, 1σ) of deformed muscovites range from 309 ± 13 to 264 ± 7 Ma, consistent with 0–16% 40 Ar ∗ loss relative to the undeformed muscovite. The in situ UV laser ablation 40 Ar/ 39 Ar ages of deformed biotite vary from 301 to 217 Ma, consistent with up to 32% 40 Ar ∗ loss. No spatial correlation is observed between in situ 40 Ar/ 39 Ar age and position within individual grains. Using available argon diffusion data for muscovite the observed 40 Ar ∗ loss in the experimentally treated muscovite can be utilized to predict average 40 Ar ∗ diffusion dimensions. Maximum 40 Ar/ 39 Ar ages obtained by UV laser ablation overlap those of the undeformed muscovite, indicating argon loss of <1% and an average effective grain radius for 40 Ar ∗ diffusion ⩾700 μm. The UV laser ablation and IR laser incremental 40 Ar/ 39 Ar ages indicating 40 Ar ∗ loss of 16% and 35%, respectively, are consistent with an average diffusion radius ≪100 μm. These results support a hypothesis of grain-scale 40 Ar ∗ diffusion distances in undeformed mica and a heterogeneous mechanical reduction in the intragrain effective diffusion length scale for 40 Ar ∗ in deformed mica. Reduction in the effective diffusion length scale in naturally deformed samples occurs most probably through production of mesoscopic and submicroscopic defects such as, e.g., stacking faults. A network of interconnected defects, continuously forming and annealing during dynamic deformation likely plays an important role in controlling both 40 Ar ∗ retention and intragrain distribution in deformed mica. Intragrain 40 Ar/ 39 Ar ages, when combined with estimates of diffusion kinetics and distances, may provide a means of establishing thermochronological histories from individual micas.

Brittany↗

USGS1982

Study of aggregative behavior of Rhinophrynus dorsalis tadpoles: design and analysis

We conducted experiments using the apparatus and design followed by Wassersug and Hessler (1971) and Wassersug (1973) to test the aggregative behavior of tadpoles of Rhinophrynus dorsalis in response to visual and olfactory stimuli. Results neither supported nor refuted the hypothesis that either stimulus is used as a mechanism for school formation. The exercise did lead to doubts about the experimental design. Some ambiguity resulted from the fact that the significance of the results depended upon the way in which the data were analyzed. Several alternative methods were considered. We also observed tadpoles reared in isolation to determine the effect of prior social conditioning on aggregative behavior. Isolates grew less than group-reared animals, were less active, and exhibited a strong avoidance reaction when subsequently exposed to conspecifics.

Herpetologica↗

USGS1992

Hydrothermal ore-forming processes in the light of studies in rock- buffered systems: II. Some general geologic applications

The experimental metal solubilities for rock-buffered hydrothermal systems, reported by Hemley et al. (1992), provide important insights into the acquisition, transport, and deposition of metals in real hydrothermal systems that produced base metal ore deposits. Water-rock reactions that determine pH, together with total chloride and changes in temperature and fluid pressure, play significant roles in controlling the solubility of metals and determining where metals are fixed to form ore deposits.Hydrothermal systems circulate fluids and heat, and the transport path of a hydrothermal fluid is likely to lie somewhere between an adiabatic (no heat loss to adjacent rocks) and a geothermal (complete thermal equilibrium with adjacent rock) path. The transport path of the hydrothermal fluids emanating from, or circulating near, deep-seated crystallizing plutons can be approximated by a quasi-adiabatic pressure-temperature path. In such a quasi-adiabatic setting, the pressure effect on rock-buffered metal solubilities is significant and allows metal transport over long distances because the trend of decreasing metal solubility with decreasing temperature is compensated by the trend of increasing metal solubility with decreasing pressure. The high-temperature portion of a quasi-adiabatic hydrothermal system will tend to leach metals from the rock and fix K and Na in feldspars. The source of the extracted metals may be late-stage magmatic melt, trace metals distributed in the lattice of silicate minerals destroyed during rock metasomatism, and/or small amounts of base metal sulfides disseminated throughout a given rock.Deposition of metals in hydrothermal systems occurs where changes such as cooling, pH increase due to rock alteration, boiling, or fluid mixing cause the aqueous metal concentration to exceed saturation. Relative metal transport concentrations, the availability of sulfur, the disposition of the saturation surfaces relative to each other, and the interplay of these variables through time are the major factors controlling the pattern of metal deposition (and nondeposition).Metal zoning results from deposition occurring at successive saturation surfaces. Zoning is not a reflection simply of relative solubility but of the manner of intersection of transport concentration paths with those surfaces. The experimental results are consistent with the typical outward zonation of Cu-Zn-Pb observed in porphyry coppers, Butte-type base metal vein deposits, skarns, and massive sulfides. Implications to mineralization patterns in Mississippi Valley-type, sedimentary Cu, and other low-temperature deposits are also of interest, with due recognition of the greater uncertainty regarding speciation and attainment of equilibrium in those environments. In such deposits, a probable outward zoning of Cu-Zn-Pb-Fe is suggested from the results.Saturation surfaces will tend to migrate outward and inward in prograde and retrograde time, respectively, controlled by either temperature or chemical variables. This, in turn, gives rise to zone migration and, where one zone encroaches on another, the appropriate apparent paragenetic relations. Such textural implications are incorrect, however, unless viewed within the context of the overall mineralization process. Additional controls bearing on metal precipitation sequence and coprecipitation, the presence or absence of zoning, reversals in zoning, sulfidation state, and timing relations between alteration and metallization are implicit in the results and are discussed.

Economic Geology↗

USGS2011

Optimization of biomass composition explains microbial growth-stoichiometry relationships

Integrating microbial physiology and biomass stoichiometry opens far-reaching possibilities for linking microbial dynamics to ecosystem processes. For example, the growth-rate hypothesis (GRH) predicts positive correlations among growth rate, RNA content, and biomass phosphorus (P) content. Such relationships have been used to infer patterns of microbial activity, resource availability, and nutrient recycling in ecosystems. However, for microorganisms it is unclear under which resource conditions the GRH applies. We developed a model to test whether the response of microbial biomass stoichiometry to variable resource stoichiometry can be explained by a trade-off among cellular components that maximizes growth. The results show mechanistically why the GRH is valid under P limitation but not under N limitation. We also show why variability of growth rate-biomass stoichiometry relationships is lower under P limitation than under N or C limitation. These theoretical results are supported by experimental data on macromolecular composition (RNA, DNA, and protein) and biomass stoichiometry from two different bacteria. In addition, compared to a model with strictly homeostatic biomass, the optimization mechanism we suggest results in increased microbial N and P mineralization during organic-matter decomposition. Therefore, this mechanism may also have important implications for our understanding of nutrient cycling in ecosystems.

American Naturalist↗

USGS2023

Interlaboratory comparison of testing hydraulic, elastic, and failure properties in compression: Lessons learned

Many geoscientific problems require us to exploit synergies of experimental and numerical approaches, which in turn lead to questions regarding the significance of experimental details for validation of numerical codes. We report results of an interlaboratory comparison regarding experimental determination of mechanical and hydraulic properties of samples from five rock types, three sandstone varieties with porosities ranging from 5% to 20%, a marble, and a granite. The objective of this study was to build confidence in the participating laboratories’ testing approaches and to establish tractable standards for several physical properties of rocks. We addressed the issue of sample-to-sample variability by investigating the variability of basic physical properties of samples of a particular rock type and by performing repeat tests. Compressive strength of the different rock types spans an order of magnitude and shows close agreement between the laboratories. However, differences among stress–strain relations indicate that the external measurement of axial displacement and the determination of system stiffness require special attention, apparently more so than the external load measurement. Furthermore, post-failure behavior seems to exhibit some machine-dependence. The different methods used for the determination of hydraulic permeability, covering six orders of magnitude for the sample suite, yield differences in absolute values and pressure dependence for some rocks but not for others. The origin of the differences in permeability, in no case exceeding an order of magnitude, correlate with the compressive strength and potentially reflect a convolution of end plug–sample interaction, sample-to-sample variability, heterogeneity on sample scale, and/or anisotropy, the last two aspects are notably not accounted for by the applied evaluation procedures. Our study provides an extensive data set apt for “benchmarking” considerations, be it regarding new laboratory equipment or numerical modeling approaches.

Environmental Earth Sciences↗

USGS1994

Variations in the chemical and stable isotope composition of carbon and sulfur species during organic-rich sediment alteration: An experimental and theoretical study of hydrothermal activity at Guaymas Basin, Gulf of California

Organic-rich diatomaceous ooze was reacted with seawater and a Na-Ca-K-Cl fluid of seawater chlorinity at 325–400°C, 400–500 bars, and fluid/sediment mass ratios of 1.56–2.35 to constrain factors regulating the abundance and stable isotope composition of C and S species during hydrothermal alteration of sediment from Guaymas Basin, Gulf of California. Alteration of inorganic and organic sedimentary components resulted in extensive exchange reactions, the release of abundant H 2 S, CO 2 , CH 4 , and C organic , to solution, and recrystallization of the sediment to an assemblage containing albitic plagioclase, quartz, pyrrhotite, and calcite. The δ 34 S cdt "> δ 34 S cdt values of dissolved H 2 S varied from −10.9 to +4.3‰ during seawater-sediment interaction at 325 and 400°C and from −16.5 to −9.0‰ during Na-Ca-K-Cl fluid-sediment interaction at 325 and 375°C. In the absence of seawater SO 4 , H 2 S is derived from both the transformation of pyrite to pyrrhotite and S released during the degradation of organic matter. In the presence of seawater SO 4 , reduction of SO 4 contributes directly to H 2 S production. Sedimentary organic matter acts as the reducing agent during pyrite and SO 4 reduction. Requisite acidity for the reduction of SO 4 is provided by Mg fixation during early-stage sediment alteration and by albite and calcite formation in Mg-free solutions. Organically derived CH 4 was characterized by δ 13 C pdb "> δ13Cpdb values ranging between −20.8 and −23.1‰, whereas δ 13 C pdb "> δ 13 C pdb values for dissolved C organic ranged between −14.8 and −17.7%. Mass balance calculations indicate that δ 13 C values for organically derived CO 2 were ≥ − 14.8%. Residual solid sedimentary organic C showed small (≤ 0.7‰) depletions in 13 C relative to the starting sediment. The experimental results are consistent with the isotopic and chemical composition of natural hydrothermal fluids and minerals at Guaymas Basin and permit us to better constrain sources and sinks for C and S species in subseafloor hydrothermal systems at sediment-covered spreading centers. Our data show that the sulfur isotope composition of hydrothermal Sulfide minerals in Guaymas Basin can be explained by derivation of S from diagenetic sulfide and seawater sulfate. Basaltic S may also contribute to hydrothermal sulfide precipitates but is not required to explain their isotopic composition. Estimates of seawater/ sediment mass ratios based on sulfur isotopic composition of sulfide minerals and the abundance of dissolved NH 3 in vent fluids range from 3–29 during hydrothermal circulation. Sources of C in Guaymas Basin hydrothermal fluids include thermal degradation of organic matter, bacteriogenic methane production, and dissolution of diagenetic carbonate.

Baja California Sur↗

USGS1990

Adsorption of selenium by amorphous iron oxyhydroxide and manganese dioxide

This work compares and models the adsorption of selenium and other anions on a neutral to alkaline surface (amorphous iron oxyhydroxide) and an acidic surface (manganese dioxide). Selenium adsorption on these oxides is examined as a function of pH, particle concentration, oxidation state, and competing anion concentration in order to assess how these factors might influence the mobility of selenium in the environment. The data indicate that 1. 1) amorphous iron oxyhydroxide has a greater affinity for selenium than manganese dioxide, 2. 2) selenite [Se(IV)] adsorption increases with decreasing pH and increasing particle concentration and is stronger than selenate [Se(VI)] adsorption on both oxides, and 3. 3) selenate does not adsorb on manganese dioxide. The relative affinity of selenate and selenite for the oxides and the lack of adsorption of selenate on a strongly acidic surface suggests that selenate forms outer-sphere complexes while selenite forms inner-sphere complexes with the surfaces. The data also indicate that the competition sequence of other anions with respect to selenite adsorption at pH 7.0 is phosphate > silicate > molybdate > fluoride > sulfate on amorphous iron oxyhydroxide and molybdate ??? phosphate > silicate > fluoride > sulfate on manganese dioxide. The adsorption of phosphate, molybdate, and silicate on these oxides as a function of pH indicates that the competition sequences reflect the relative affinities of these anions for the surfaces. The Triple Layer surface complexation model is used to provide a quantitative description of these observations and to assess the importance of surface site heterogeneity on anion adsorption. The modeling results suggest that selenite forms binuclear, innersphere complexes with amorphous iron oxyhydroxide and monodentate, inner-sphere complexes with manganese dioxide and that selenate forms outer-sphere, monodentate complexes with amorphous iron oxyhydroxide. The heterogeneity of the oxide surface sites is reflected in decreasing equilibrium constants for selenite with increasing adsorption density and both experimental observations and modeling results suggest that manganese dioxide has fewer sites of higher energy for selenite adsorption than amorphous iron oxyhydroxide. Modeling and interpreting the adsorption of phosphate, molybdate, and silicate on the oxides are made difficult by the lack of constraint in choosing surface species and the fact that equally good fits can be obtained with different surface species. Finally, predictions of anion competition using the model results from single adsorbate systems are not very successful because the model does not account for surface site heterogeneity. Selenite adsorption data from a multi-adsorbate system could be fit if the equilibrium constant for selenite is decreased with increasing anion adsorption density.

Geochimica et Cosmochimica Acta↗

USGS2013

Electrical signatures of ethanol-liquid mixtures: implications for monitoring biofuels migration in the subsurface

Ethanol (EtOH), an emerging contaminant with potential direct and indirect environmental effects, poses threats to water supplies when spilled in large volumes. A series of experiments was directed at understanding the electrical geophysical signatures arising from groundwater contamination by ethanol. Conductivity measurements were performed at the laboratory scale on EtOH–water mixtures (0 to 0.97 v/v EtOH) and EtOH–salt solution mixtures (0 to 0.99 v/v EtOH) with and without a sand matrix using a conductivity probe and a four-electrode electrical measurement over the low frequency range (1–1000 Hz). A Lichtenecker–Rother (L–R) type mixing model was used to simulate electrical conductivity as a function of EtOH concentration in the mixture. For all three experimental treatments increasing EtOH concentration resulted in a decrease in measured conductivity magnitude (|σ|). The applied L–R model fitted the experimental data at concentration ≤ 0.4 v/v EtOH, presumably due to predominant and symmetric intermolecular (EtOH–water) interaction in the mixture. The deviation of the experimental |σ| data from the model prediction at higher EtOH concentrations may be associated with hydrophobic effects of EtOH–EtOH interactions in the mixture. The |σ| data presumably reflected changes in relative strength of the three types of interactions (water–water, EtOH–water, and EtOH–EtOH) occurring simultaneously in EtOH–water mixtures as the ratio of EtOH to water changed. No evidence of measurable polarization effects at the EtOH–water and EtOH–water–mineral interfaces over the investigated frequency range was found. Our results indicate the potential for using electrical measurements to characterize and monitor EtOH spills in the subsurface.

Journal of Contaminant Hydrology↗

USGS2018

Suppression of vitrinite reflectance by bitumen generated from liptinite during hydrous pyrolysis of artificial source rock

Mean random vitrinite reflectance (R o ) is the most widely accepted method to determine thermal maturity of coal and other sedimentary rocks. However, oil-immersion R o of polished rock or kerogen samples is commonly lower than R o values measured in samples from adjacent vitrinite-rich coals that have undergone the same level of thermal stress. So-called suppressed R o values have also been observed in hydrous pyrolysis experiments designed to simulate petroleum formation. Various hypotheses to explain R o suppression, such as sorption of products generated from liptinite during maturation, diagenetic formation of perhydrous vitrinite or overpressure, remain controversial. To experimentally test for suppression of vitrinite reflectance, artificial rock was prepared using silica and a calcined blend of limestone and clay with various proportions of thermally immature vitrinite-rich Wyodak-Anderson coal and liptinite-rich kerogen isolated from the oil-prone Parachute Creek Member of the Green River Formation. The samples were subjected to hydrous pyrolysis for 72 h. at isothermal temperatures of 300 °C, 330 °C, and 350 °C to simulate burial maturation. Compared to artificial rock that contains only coal, samples with different proportions of oil-prone kerogen show distinct suppression of calibrated R o at 300 °C and 330 °C. The reflectance of solid bitumen generated during heating of the samples is lower than that of the associated vitrinite and does not interfere with the R o measurements. These results provide the first experimental evidence that R o suppression occurs in vitrinite mixed with liptinite-rich kerogen in a rock matrix. Although the precise chemical mechanism for R o suppression by liptinite remains unclear, free radicals generated from solid bitumen and associated volatile products during maturation of liptinite may contribute to termination reactions that slow the aromatization and rearrangement of polyaromatic sheets in vitrinite, thus suppressing R o . This mechanism does not preclude R o suppression that might result from overpressure or differences in redox conditions during diagenesis.

Organic Geochemistry↗

USGS2023

Resource-driven pattern formation in consumer-resource systems with asymmetric dispersal on a plane

This paper considers resource-driven pattern formation in consumer-resource systems. Here, a planar pattern consists of many big patches, and a big patch can be regarded as combination of many patches on the plane. The consumer moves between patches asymmetrically, while the asymmetry is driven by the resource abundance. Based on experimental models with linearly-linked patches, we propose a planarly-linked-patch model with asymmetric dispersal. Using dynamical systems theory, we show global stability of equilibria in the model, and demonstrate how the resource-driven dispersal forms patterns. It is shown that appropriate asymmetry in dispersal would make the consumer persist in the system, even in sink patches. The asymmetry could also make the consumer’s total population abundance larger than that without dispersal. However, inappropriate asymmetry would make the consumer go into extinction, even in source patches. Dispersal rates are also shown to play a role in the persistence and abundance increase. Our results are consistent with experimental observations and provide new insights. Numerical simulations by the model reproduce various vegetation patterns in the real world. This work has potential applications in spatial pattern formation in biological research.

SIAM Journal on Applied Mathematics↗

USGS1983

Effects of oil on avian reproduction: A review and discussion

Oil pollution is a highly visible form of environmental contamination that affects avian reproduction in a variety of ways. Plumage oiling causes widespread and locally severe mortality of adult birds. Egg oiling can be a serious hazard for bird embryos but only a few field observationons of this have been reported. Oil ingestion seldom kills birds directly but it causes sublethal change~ in the bodily functions and behavior of adults and nestlings. Studies of the effects of oil on avian reproduction have produced varied and, in ingestion studies, sometimes conflicting results because of inconsistent experimental design and the use of different test species and types of oil. Field experimentation with the sublethal effects of ingested oil on avian reproduction has been limited. Simulation modelling of seabird populations has shown that (l) an occasional decrease in survival of breeding adults will have a greater impact on seabird populations than an occasional decrease in reproductive success, and (2) populations of long-lived seabirds with low reproductive potential have great difficulty recovering from high one-time mortality when experiencing even small sustained annual decreases in either natality or breeding adult survival. The impact of oil-related decreases in survival or reproduction will be more noticeable at the local or colony level than at the regional or species level. Immigration, surplus breeders, and possible compensatory changes in natality and mortality resulting from population reductions usually prevent local population reductions from lasting very long (unless the species is rare or at the edge of its range). A study of west European seabird populations indicates that the natural annual mortality of the region greatly exceeds the annual mortality due to plumage oiling; effects of oil ingestion and egg oiling were not measured but were thought to be less than the mortality from plu~age oiling. Oil-related mortality, even if in addition to expected mortality, would not have a detectable impact on regional populations if environmental conditions were favorable (increased natality, decreased mortality) for the birds.

Book chapter↗

USGS2019

Comparisons of stereological and other approaches for quantifying macrophage aggregates in piscine spleens

Macrophage aggregates (MA s) are focal accumulations of pigmented macrophages in the spleen and other tissues of fish. A central role of MA s is the clearance and destruction of degenerating cells and recycling of some cellular components. Macrophage aggregates also respond to chemical contaminants and infectious agents and may play a role in the adaptive immune response. Tissue damage or physiological stress can result in increased MA accumulation. As a result, MA s may be sensitive biomarkers of environmental stress in fish. Abundance of MA s in tissues has been reported in a variety of ways—most commonly as density, mean size, and relative area—but the utility of these estimates has not been compared. In this study, four different types of splenic MA abundance estimates (abundance score, density, relative area, and total volume) were compared in two fish populations (Striped Bass Morone saxatilis and White Perch M. americana ) with a wide range in ages. Stereological estimates of total volume indicated an increase in MA abundance with spleen volume, which generally corresponded to fish age, and with splenic infections (mycobacteria or trematode parasites). Abundance scores were generally limited in the ability to detect changes in MA abundance by these factors, whereas density estimates were greatly influenced by changes in spleen volume. In some instances, densities declined while the total volume of MA s and spleen volume increased. Experimentally induced acute stress resulted in a decrease in spleen volume and an increase in MA density, although the total volume of MA s remained unchanged. Relative area estimates accounted for the size and number of MA s but not for changes in organ volume. Total volume is an absolute measure of MA abundance irrespective of changes in organ volume or patterns of accumulation and may provide an improved means of quantifying MA s in the spleens of fish.

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